1,8-naphthalimide derivative, preparation method therefor and use thereof

ABSTRACT

Disclosed are a 1,8-naphthalimide derivative, a preparation method therefor and a use thereof. The 1,8-naphthalimide derivative is easy to prepare, and is an enhanced Cu2+ fluorescent probe, which can detect Cu2+ by two wavelengths and be applied to almost-all-water systems. According to atitration experiments and blank experiments at 392 nm and 754 nm, the detection limit of the 1,8-naphthalimide derivative of the present invention for Cu2+ is 2.6368×10−7 mol/L and 2.0156×10−7 mol/L, respectively, indicating that same can perform quantitative detection for Cu2+ with a high selectivity and a high sensitivity by using two wavelengths. In addition, a pH colorimetric switch based on 1,8-naphthalimide can rapidly and reversibly respond to a pH by means of three ways: a maximum absorption wavelength, absorbance and color change. Same has a narrow switching pH range, a good selectivity and a high sensitivity, can be used in almost-all-water systems.

FIELD OF THE INVENTION

The present invention belongs to the technical field of fluorescent probes, and specifically relates to a 1,8-naphthalimide derivative, a preparation method therefor and a use thereof.

BACKGROUND OF THE INVENTION

1,8-naphthalimide compounds under light will undergo intramolecular charge transfer between a substituent at the 4-position C of a naphthalene ring and an iminocarbonyl, which will result in changes in fluorescence emission wavelength and fluorescence intensity; besides, they have strong photostability, high fluorescence quantum yield, large Stokes shift, and easy molecular structure modification. Therefore, they are widely used in fiber dyeing, fluorescence recognition and labeling, photoelectric materials and other different fields. For the 1,8-naphthalimide compounds, different modifications will bring different effects and applications. For example, structure 1 is a fluorescent dye for fibers, structure 2 is a Hg²⁺ fluorescent probe, and structure 3 is used as a photoelectric material.

Cu²⁺, as a trace element, plays an important role in human life activities. The deficiency of Cu²⁺ will cause various problems of blood, nervous system, etc.; however, excessive Cu²⁺ can also be potentially toxic to human living cells, and lead to cardiovascular and neurodegenerative diseases including Wilson's disease, Alzheimer's disease, prion diseases, and so on. In recent years, the content of Cu²⁺ in many water bodies has exceeded the standard seriously due to excessive discharge of factories and other reasons. According to the Environmental Protection Agency (EPA), the maximum concentration of Cu²⁺ in drinking water must not exceed 20 μM (R. Shen, J. J. Yang, H. Luo, B. Wang, Y. Jiang. A sensitive fluorescent probe for cysteine and Cu²⁺ based on 1,8-naphthalimide derivatives and its application in living cells imaging. Tetrahedron 73 (2017) 373-377). Therefore, it is very important to detect Cu²⁺ in biological and environmental systems. Using fluorescent probes to detect heavy metal ions has the advantages of simple method, low cost, high sensitivity, good selectivity, and quick response. Some fluorescent probes have been used to detect Cu′. In summary, most of the Cu²⁺ fluorescent probes based on 1,8-naphthalimide are of a quenching type and have low sensitivity; moreover, some of them have complex structure and are difficult to synthesize, some of them have weak anti-interference ability, and some of them can only be used in an organic solvent system and have poor practicability.

As an important parameter in many chemical and biological processes, pH plays a vital role in chemical reactions, natural environment, biological cells and tissue activities (J. Chao, H. Wang, Y. Zhang, C. Yin, F. Huo, K. Song, Z. Li, T. Zhang, Y. Zhao. A novel ‘donor-π-acceptor’ type fluorescence probe for sensing pH: mechanism and application in vivo. Talanta 174 (2017) 468-476). For example, pH can be used to regulate chemical reactions, strong acids and bases may cause corrosion and burns, and abnormal pH may cause cardiopulmonary and neurological diseases. Therefore, monitoring pH is of great significance. The ultraviolet-visible (UV-Vis) absorption spectrum is favored by people because of its advantages such as fast response, high sensitivity, and visual recognition of signal response. The indication of signal change by the pH colorimetric switch that uses UV-Vis absorption spectrum to respond to pH mutation is usually discernible to the naked eye. It can display the pH change in the organism or environment in the most direct way, and is thus very meaningful to get studied. However, some existing pH colorimetric switches can only be used in strong acid or alkali systems, some have low sensitivity, some have a wide pH range for switching, and some have weak anti-interference ability. The pH colorimetric switch with excellent comprehensive performance needs to be developed urgently.

CONTENTS OF THE INVENTION

The enhanced Cu²⁺ fluorescent probe based on 1,8-naphthalimide disclosed in the present invention has the advantages of high selectivity, high sensitivity, strong anti-interference ability, relatively easy synthesis, and application in almost-all-water systems. Besides, the present invention discloses a pH colorimetric switch based on 1,8-naphthalimide, which is relatively easy to synthesize, can respond to a pH by means of three ways, has a narrow switching pH range, responds rapidly and reversibly, and can be used in almost-all-water systems.

The present invention adopts the following technical solution:

A preparation method for a 1,8-naphthalimide derivative is provided, comprising the following steps:

(1) preparing an intermediate A using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials;

(2) preparing an intermediate B using the intermediate A and hydrazine hydrate as raw materials;

(3) preparing an intermediate C using the intermediate B and glyoxal as raw materials; and

(4) preparing the 1,8-naphthalimide derivative using the intermediate C and trihydroxymethyl aminomethane as raw materials.

A Cu²⁺ fluorescent probe system and a preparation method therefor, the method comprising the following steps:

(1) preparing an intermediate A using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials;

(2) preparing an intermediate B using the intermediate A and hydrazine hydrate as raw materials;

(3) preparing an intermediate C using the intermediate B and glyoxal as raw materials;

(4) preparing the 1,8-naphthalimide derivative using the intermediate C and trihydroxymethyl aminomethane as raw materials; and

(5) adding the 1,8-naphthalimide derivative to a solvent to prepare the Cu²⁺ fluorescent probe system, the solvent being an organic solvent and/or water.

In step (5) of the above technical solution, the organic solvent is acetonitrile; when the solvent is an organic solvent and water, the volume ratio of the organic solvent to water is less than or equal to 1/99.

A method for detecting the content of Cu²⁺ in the system is provided, comprising the following steps:

(1) preparing an intermediate A using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials;

(2) preparing an intermediate B using the intermediate A and hydrazine hydrate as raw materials;

(3) preparing an intermediate C using the intermediate B and glyoxal as raw materials;

(4) preparing the 1,8-naphthalimide derivative using the intermediate C and trihydroxymethyl aminomethane as raw materials; and

(5) adding the 1,8-naphthalimide derivative solution to the system, measuring fluorescence intensity, and then determining the content of Cu²⁺ in the system according to a curve of relationship between the fluorescence intensity and the concentration of Cu²⁺ in the system.

In the above technical solution, the final concentration of the 1,8-naphthalimide derivative is 10 μM.

When the 1,8-naphthalimide derivative of the present invention is used as a Cu²⁺ fluorescent probe, the detection environment may be an organic solvent environment and/or a water environment; that is, the 1,8-naphthalimide derivative can be used to detect copper ions in water or a mixture of water and an organic solvent.

In step (1) of the present invention, the molar ratio of 4-bromo-1,8-naphthalic anhydride to n-butylamine is 1:1.3, and the intermediate A is prepared using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials in the presence of the organic solvent and under the protection of nitrogen. For example, under the protection of N₂, stirring 4-bromo-1,8-naphthalic anhydride and n-butylamine with acetic acid as the solvent to react at 120° C. for 6 h, then stopping the reaction, pouring the reaction solution into ice water to precipitate a light yellow solid, filtering, recrystallizing the filter cake with ethanol, and drying in vacuum to obtain a light yellow solid intermediate A.

In step (2) of the present invention, the molar ratio of the intermediate A to hydrazine hydrate is 1:5.3, and the intermediate B is prepared using the intermediate A and hydrazine hydrate as raw materials in the presence of the organic solvent. For example, refluxing the intermediate A and hydrazine hydrate with glycol monomethyl ether as the solvent to react at 125° C. for 5 h, then cooling to room temperature, pouring into 50 mL of water and stand still to form an orange-red precipitate, filtering, washing the filter cake twice with deionized water, and washing again with a small amount of ethanol, and then drying in vacuum to obtain an orange-red solid powder intermediate B.

In step (3) of the present invention, the molar ratio of the intermediate B to glyoxal is 1:(13.3 to 15.5), and the intermediate C is prepared using the intermediate B and glyoxal as raw materials in the presence of organic solvent. For example, stirring the intermediate B and glyoxal with anhydrous ethanol as the solvent to react at room temperature for 6 h, then stopping reaction, precipitate an orange solid, filtering, washing the filter cake once with ethanol and then twice with deionized water, and then drying in vacuum to obtain an orange intermediate C.

In step (4) of the present invention, the molar ratio of the intermediate C to trihydroxymethyl aminomethane is 1:(1 to 1.6), and the 1,8-naphthalimide derivative is prepared using the intermediate C and trihydroxymethyl aminomethane as raw materials in the presence of organic solvent. For example, making the intermediate C and trihydroxymethyl aminomethane react with one of anhydrous ethanol, anhydrous methanol and dichloromethane as the solvent at 25° C. to 80° C. for 6 h to 24 h, then removing the solvent by rotary evaporation, dispersing the residue in 10 mL of dichloromethane, filtering with suction to obtain an orange-red solid crude product, and then washing the crude product three times alternately and respectively with dichloromethane and deionized water to obtain an orange-red solid 1,8-naphthalimide derivative.

In the present invention, obtaining the curve of relationship between the fluorescence intensity and the concentration of Cu²⁺ is a conventional technique. Standard solutions with different concentrations of Cu²⁺ are prepared, and the fluorescence intensity of each standard solution is measured with the 1,8-naphthalimide derivative, respectively, and then a standard curve of Cu²⁺ concentration-fluorescence intensity is obtained according to the relationship between the concentration and the fluorescence intensity.

The 1,8-naphthalimide derivative prepared in the present invention has the following chemical structural formula:

The 1,8-naphthalimide derivative of the present invention can have high selectivity and sensitivity to Cu²⁺ by means of two wavelengths. Therefore, the present invention also discloses the use of the above 1,8-naphthalimide derivative as a Cu²⁺ fluorescent probe, or the use of the Cu²⁺ fluorescent probe system in detecting Cu²⁺, with the application environment being an organic solvent and/or water environment.

The present invention also discloses the use of the above 1,8-naphthalimide as a pH colorimetric switch.

The present invention also discloses the use of the above 1,8-naphthalimide in the preparation of pH colorimetric switch materials.

The present invention also discloses a 1,8-naphthalimide-based pH colorimetric switch system comprising the above 1,8-naphthalimide and a solvent, the solvent being an organic solvent and/or water.

The present invention also discloses the use of the above 1,8-naphthalimide-based pH colorimetric switch system in pH colorimetry.

The present invention also discloses the use of the above 1,8-naphthalimide-based pH colorimetric switch system in the preparation of pH colorimetric switch materials.

A method for pH colorimetry of a solution to be tested is provided, comprising the following steps: Adding the above 1,8-naphthalimide solution to the solution to be tested to obtain a mixed system, then testing the UV-Vis(ultraviolet-visible) absorption spectrum of the mixed system, and completing the pH colorimetry of the solution to be tested according to color of the mixed system, UV-Vis absorption wavelength, and absorbance. The concentration of 1,8-naphthalimide in the mixed system of the above technical solution is 10 μM; when the mixed system contains an organic solvent and water, the volume ratio of the organic solvent to water is less than 4. In the present invention, the environment for the use of 1,8-naphthalimide in pH colorimetry is an organic solvent and/or water environment. That is, when the 1,8-naphthalimide of the present invention is used as a pH colorimetric switch, the application environment may be an organic solvent, water, or a mixed environment of an organic solvent and water; and in the mixed environment of an organic solvent and water, the volume ratio of the organic solvent to water is less than 4, or even down to 1/99.

The preparation method of the present invention can be expressed as follows:

The present invention designs and synthesizes a novel 1,8-naphthalimide derivative BNGT, which is relatively easy to prepare, and is an enhanced Cu²⁺ fluorescent probe that can detect Cu²⁺ by means of two wavelengths, and can be especially applied to almost-all-water systems. According to atitration experiments and blank experiments at 392 nm and 754 nm, the detection limit of BNGT for Cu²⁺ is 2.6368×10⁻⁷ mol/L and 2.0156×10⁻⁷ mol/L, respectively, indicating that BNGT can perform quantitative detection for Cu²⁺ with a high selectivity and a high sensitivity by using two wavelengths. The 1,8-naphthalimide of the present invention can rapidly and reversibly respond to a pH by means of three ways: a maximum absorption wavelength, absorbance and color change. Same has a narrow switching pH range (from a pH of 5.8 to a pH of 6.0, only 0.2 pH units), a good selectivity and a high sensitivity, can be used in almost-all-water systems, and has a bright application prospective.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the response of the fluorescence spectrum of BNGT to different metal ions;

FIG. 2 shows the fluorescence spectrum of a BNGT solution (10 μM) with different concentrations of Cu²⁺;

FIG. 3 shows the effect of coexisting metal ions on the fluorescence intensity of a BNGT solution containing Cu²⁺;

FIG. 4 shows the UV-Vis absorption spectrum of BNGT at different pHs;

FIG. 5 shows the UV-Vis absorption spectrum of BNGT at different pHs;

FIG. 6 shows the UV-Vis absorption spectrum of BNGT at different pHs;

FIG. 7 shows the maximum absorption wavelength and color of BNGT at different pHs;

FIG. 8 shows the speed of response of the maximum absorption wavelength and color of BNGT to pH;

FIG. 9 shows the speed of response of the absorbance of BNGT to pH;

FIG. 10 shows the effect of coexisting metal ions on the maximum absorption wavelength and color of the BNGT solution;

FIG. 11 shows the effect of coexisting metal ions on the absorbance of the BNGT solution;

FIG. 12 shows the reversibility of response of the maximum absorption wavelength and color of BNGT to pH; and

FIG. 13 shows the reversibility of response of the absorbance of BNGT to pH.

DETAILED DESCRIPTION OF THE EMBODIMENTS Example 1: Preparation of Intermediate A

Adding 4-bromo-1,8-naphthalic anhydride and n-butylamine in a molar ratio of 1:1.3 to acetic acid, and stirring them to react at 120° C. for 6 h under the protection of N₂, then stopping the reaction, pouring the reaction solution into ice water to precipitate a light yellow solid, filtering, recrystallizing the filter cake with ethanol, and drying in vacuum to obtain a light yellow solid intermediate A at a yield of 85.0%.

Example 2: Preparation of Intermediate B

Adding the intermediate A and hydrazine hydrate in a molar ratio of 1:5.3 to glycol monomethyl ether, and refluxing them to react at 125° C. for 5 h, then cooling to room temperature, pouring into 50 mL of water and stand still to form an orange-red precipitate, filtering, washing the filter cake twice with deionized water, and washing again with a small amount of ethanol, and then drying in vacuum to obtain an orange-red solid powder intermediate B at a yield of 87.7%.

Example 3: Preparation of Intermediate C

Adding the intermediate B and glyoxal in a molar ratio of 1:13.3 to anhydrous ethanol and stirring at room temperature for 6 h, then stopping the reaction to precipitate an orange solid, filtering, washing the filter cake once with ethanol and then twice with deionized water, and then drying in vacuum to obtain an orange intermediate C at a yield of 66.0%.

Adding the intermediate B and glyoxal in a molar ratio of 1:14 to anhydrous ethanol and stirring at room temperature for 6 h, then stopping the reaction to precipitate an orange solid, filtering, washing the filter cake once with ethanol and then twice with deionized water, and then drying in vacuum to obtain an orange intermediate C at a yield of 70.0%.

Adding the intermediate B and glyoxal in a molar ratio of 1:15.5 to anhydrous ethanol and stirring at room temperature for 6 h, then stopping the reaction to precipitate an orange solid, filtering, washing the filter cake once with ethanol and then twice with deionized water, and then drying in vacuum to obtain an orange intermediate C at a yield of 71.0%.

Example 4: Preparation of 1,8-Naphthalimide Derivative

Making the intermediate C (referred to as BNG) and trihydroxymethyl aminomethane in a molar ratio of 1:1.6 react at 50° C. for 7 h with anhydrous ethanol as the solvent under the protection of N₂, then cooling to room temperature, removing the solvent by rotary evaporation, dispersing the residue in 10 mL of dichloromethane, filtering with suction to obtain an orange-red solid crude product, and then washing the crude product three times alternately and respectively with dichloromethane and deionized water to obtain an orange-red powder target product 1,8-naphthalimide derivative called BNGT at a yield of 75.0%. Other synthesis conditions and corresponding yields of BNGT are shown in Table 1.

TABLE 1 Other synthesis conditions and corresponding yields of BNGT Molar ratio of BNG Reaction Reaction Under the to trihydroxymethyl temperature time protection Yield No. aminomethane Solvent (° C.) (h) of N₂ (%) 1 1:1.0 Anhydrous 80 6 Yes 50.8 ethanol 2 1:1.4 Anhydrous 80 6 Yes 54.2 ethanol 3 1:1.6 Anhydrous 80 6 Yes 60.0 ethanol 4 1:1.6 Anhydrous 60 6 Yes 71.4 ethanol 5 1:1.6 Anhydrous 50 6 Yes 73.5 ethanol 6 1:1.6 Anhydrous 25 6 Yes 30.5 ethanol 7 1:1.6 Anhydrous 50 7 Yes 75.0 ethanol 8 1:1.6 Anhydrous 50 10 Yes 73.2 ethanol 9 1:1.6 Anhydrous 50 24 Yes 72.1 ethanol 10 1:1.6 Dichloro- 50 7 Yes 15.5 methane 11 1:1.6 Anhydrous 50 7 Yes 45.0 ethanol

Characterization of BNGT:

IR (KBr) cm⁻¹: 3441.56 (—OH), 2871.48, 2930.70, 2959.43 (CH₃, CH₂), 1687.05 (C═N), 1639.67 (C═O), 1388.96, 1426.57, 1585.09 (ArH), 1116.97 (C—N). ¹H NMR (DMSO-d₆, 400 MHz): δ ppm 0.91-0.95 (t, 3H, CH₃), 1.34-1.36 (m, 2H, CH₂), 1.59-1.60 (m, 2H, CH₂), 3.60-3.62 (m, 2H, CH₂), 4.00 (s, 2H, CH₂), 4.50-5.08 (m, 3H, OH), 7.51-7.53 (d, 1H, J=8.4, ArH), 7.77-7.79 (m, 1H, CH), 7.82-7.87 (m, 1H, ArH), 8.40-8.42 (d, 1H, J=8.4, CH), 8.48-8.50 (m, 1H, ArH), 8.68-8.73 (t, 1H, J=8.4 Hz, ArH), 9.62-9.64 (d, 1H, J=8, ArH), 12.21 (s, 1H, NH). ¹³C NMR (DMSO-d₆, 400 MHz) δ: 163.95, 163.07, 146.83, 140.34, 133.15, 131.69, 128.28, 126.30, 122.60, 120.04, 114.87, 111.46, 109.46, 67.47, 61.58, 39.04, 29.85, 19.90, 13.70. LC-MS m/z calcd. C₂₂H₂₆N₄O₅: theoretical value: 426.19 [M+H]⁺, experimental value: 426.19. Anal. Calcd. C₂₂H₂₆N₄O₅: (426.19) theoretical value: C: 61.96, N: 13.14, H: 6.15, experimental value: C: 61.61, N: 12.75, H: 6.15.

The above preparation method can be expressed as follows:

Example 5: Selectivity and Sensitivity of BNGT to Cu²⁺

Adding Fe³⁺, K⁺, Na⁺, Mg²⁺, Ni²⁺, Ag⁺, Cr³⁺, Cd²⁺, Co²⁺, Zn²⁺, Mn²⁺, Fe²⁺, Cu²⁺, Ca²⁺, Hg²⁺ and Pb²⁺ respectively to the acetonitrile/water (in a volume ratio of 1/99) solution of BNGT, and obtaining the fluorescence spectrum before and after the addition of metal ions, with the results as shown in FIG. 1; solvent: acetonitrile/water (in a volume ratio of 1/99); concentration: BNGT 10 metal ions 100 μm; excitation wavelength: 345 nm; slot width: 5 nm; temperature: 25° C. It can be seen that only Cu²⁺ could enhance the fluorescence intensity of the BNGT solution, which was 9.2 times stronger at a wavelength of 392 nm and 9.4 times stronger at a wavelength of 754 nm; the bright blue could be seen under a UV lamp, indicating that BNGT in acetonitrile/water (in a volume ratio of 1/99) could have high selectivity and sensitivity to Cu²⁺ by using two wavelengths, and did not respond to other individual metals.

Example 6: Linear Range and Detection Limit of Cu²⁺ Detected by BNGT

FIG. 2 shows the fluorescence spectrum of a BNGT solution (with acetonitrile/water as the solvent in a volume ratio of 1/99) with different concentrations of Cu²⁺; excitation wavelength: 345 nm; slot width: 5 nm; temperature: 25° C.; concentrations of Cu²⁺ from bottom to top: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 30, 40, 50, 75 and 100 μM. The insets show the relationship between the maximum fluorescence intensity of the BNGT solution and the concentration of Cu²⁺ at 392 nm and 754 nm, respectively. As can be seen from FIG. 2, when the concentration of Cu²⁺ was in the range of 0 to 20 μM, the fluorescence intensity of BNGT at wavelengths of 392 nm and 754 nm had a good linear relationship with the concentration of Cu²⁺, the linear equations being F=109170.7529×[Cu²⁺]+530079.7583 and F=10677.1606×[Cu²⁺]+50519.5202, the correlation coefficients being R=0.9928 and R=0.9930, respectively. According to atitration experiments and blank experiments at 392 nm and 754 nm, the detection limit of BNGT for Cu²⁺ was 2.6368×10⁻⁷ mol/L and 2.0156×10⁻⁷ mol/L, respectively, indicating that BNGT could perform quantitative detection for Cu²⁺ with a high selectivity and a high sensitivity by using two wavelengths.

Example 7: Effects of Coexisting Ions on Detection of Cu²⁺ by BNGT

FIG. 3 shows the effect of environmentally and biologically relevant metal ions on the maximum fluorescence intensity of a BNGT solution (with acetonitrile/water as the solvent in a volume ratio of 1/99) containing Cu²⁺ at 392 nm and 754 nm; solvent: acetonitrile/water (in a volume ratio of 1/99); concentration: BNGT 10 μM, metal ions 100 μM; excitation wavelength: 345 nm; slit width: 5 nm; temperature: 25° C. It can be seen that the addition of Mg²⁺, K⁺, Na⁺, Ag⁺, Cr³⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Ca²⁺, Pb²⁺ and Hg²⁺ (100 μM) had little effect on the maximum fluorescence intensity of the solution. The results show that BNGT in acetonitrile/water in a volume ratio of 1/99 had strong anti-interference ability in detecting Cu²⁺.

Example 8: Analysis of Cu²⁺ in Spiked Water Samples

In order to investigate the practicality of BNGT in the actual environment, BNGT was used to carry out the spiked analysis of the pond water and tap water of Dushu Lake Campus of Soochow University. The specific implementation method of the detection was as follows: Taking respectively 1 mL of the sample to be tested, adding 100 μL of 1 mM BNGT solution with acetonitrile as the solvent, then respectively adding 15 μM and 20 μM Cu²⁺, and making up to volume with deionized water to obtain the solution to be tested in acetonitrile/water (in a volume ratio of 1/99) with the concentration of BNGT at 10 μM; exciting at a slit width of 5 nm with 345 nm as the excitation wavelength, and measuring the fluorescence spectrum of the solution; and obtaining the concentration of Cu²⁺ in the water sample to be measured according to the linear relationship between the maximum fluorescence intensity of BNGT and the concentration of Cu²⁺ (as shown in the inset in FIG. 2). The results were shown in Table 2. The concentration of Cu²⁺ measured at 392 nm and 754 nm was close to the concentration of Cu²⁺ added in the system, the recovery rate of Cu²⁺ was between 97.13% and 103.45%, and the relative standard deviation of the three parallel experiments was less than 1.58%. Therefore, BNGT could be used to effectively detect Cu²⁺ in actual environmental water samples by means of two wavelengths.

TABLE 2 Recovery rate of Cu²⁺ in pond water and tap water (3 parallel determinations) Wavelength 392 nm Wavelength 754 nm Relative Relative Recovery standard Recovery standard Added Detected rate deviation Detected rate deviation Sample Cu²⁺ Cu²⁺ (%) (%) Cu²⁺ (%) (%) Pond 15 14.77 98.47 0.59 14.57 97.13 1.10 water 20 20.69 103.45 0.72 20.13 100.65 0.71 Tap 15 14.96 99.73 1.00 14.80 98.67 1.35 water 20 20.31 101.55 1.58 20.40 102.00 0.66

Solvent: acetonitrile/water (in a volume ratio of 1/99); concentration: BNGT 10 μM; concentration unit of Cu²⁺: 10⁻⁶ mol/L.

The compound designed and synthesized by the present invention is relatively easy to synthesize, can detect Cu²⁺ with a good selectivity and a high sensitivity by means of two wavelengths and enhanced fluorescence, can be applied to almost-all-water systems, and has good practicability and a bright application prospective.

Example 9: Response of BNGT to pH

Preparing a 1.0×10⁻³ mol/L BNGT stock solution with acetonitrile as a solvent, and transferring 100 μL of the BNGT stock solution respectively into three series of 10 mL volumetric flasks; adding 7 mL of deionized water to the first series of volumetric flasks, adding 2 mL of deionized water and 5 ml of acetonitrile to the second series of volumetric flasks, and adding 1 mL of deionized water and 8 ml of acetonitrile to the third series of volumetric flasks; then titrating to the desired pH value respectively with 0.1 M NaOH and 0.1 M HCl aqueous solutions, and finally making up to volume with deionized water to obtain an acetonitrile/water solution of BNGT with different pHs in three solvent systems, the volume ratios of acetonitrile/water in the three solvent systems being 1/99, 1/1 and 8/2, respectively.

The responses of UV-Vis absorption spectra of BNGT (with acetonitrile/water as the solvent in a volume ratio of 1/99, 1/1 and 8/2) to different pHs were investigated, respectively, as shown in FIGS. 4, 5 and 6.

FIG. 4 shows the UV-Vis absorption spectrum of BNGT (with acetonitrile/water as the solvent in a volume ratio of 1/99) in a pH range of 1.9 to 12.0; solvent: acetonitrile/water (in a volume ratio of 1/99); concentration: BNGT 10 μM; pH: 1.9, 3.1, 4.0, 5.0, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.5, 8.0, 9.0, 9.8, 11.2, 12.0. As can be concluded from the figure, when the pH was in the range of 1.9 to 5.8, the maximum absorption wavelength of BNGT was around 432 nm, and the absorbance was at a low level; when the pH was in the range of 6.0 to 12.0, the maximum absorption wavelength was about 527 nm, and the absorbance increased significantly; when pH changed from 5.8 to 6.0, the solution changed from colorless to red, and the maximum absorption wavelength and absorbance changed suddenly, the maximum wavelength red-shifting by 95 nm, the absorbance at 527 nm increasing by about 6 times.

FIG. 5 shows the UV-Vis absorption spectrum of BNGT (with acetonitrile/water as the solvent in a volume ratio of 1/1) at different pHs; solvent: acetonitrile/water (in a volume ratio of 1/1); concentration: BNGT 10 μM; pH: 1.9, 3.1, 4.0, 5.0, 5.8, 6.0, 6.3, 6.6, 6.8, 7.0, 8.0, 9.0, 9.8, 11.2, 12.0. As can be seen from the figure, when the pH was in the range of 1.9 to 5.8, the maximum absorption wavelength of BNGT was around 420 nm; when the pH was in the range of 6.0 to 12.0, the maximum absorption wavelength was around 535 nm; when pH changed from 5.8 to 6.0, the solution changed from colorless to red, and the maximum absorption wavelength and absorbance changed suddenly, the maximum absorption wavelength red-shifting by 115 nm, the absorbance at 535 nm increasing by about 20 times.

FIG. 6 shows the UV-Vis absorption spectrum of BNGT (with acetonitrile/water as the solvent in a volume ratio of 8/2) at different pHs; solvent: acetonitrile/water (in a volume ratio of 8/2); concentration: BNGT 10 μM; pH: 1.9, 3.1, 4.0, 5.0, 5.8, 6.0, 6.3, 6.6, 6.8, 7.0, 8.0, 9.0, 9.8, 11.2, 12.0. As can be seen from the figure, when the pH was in the range of 1.9 to 5.8, the maximum absorption wavelength of BNGT was around 422 nm; when the pH was in the range of 6.0 to 12.0, the maximum absorption wavelength was around 537 nm; when pH changed from 5.8 to 6.0, the solution changed from colorless to red, and the maximum absorption wavelength and absorbance changed suddenly, the maximum absorption wavelength red-shifting by 115 nm, the absorbance at 537 nm increasing by about 28 times.

As can be seen, in a very narrow pH range (pH 5.8 to 6.0), all the BNGT solutions with acetonitrile/water as the solvent in three different volume ratios had obvious sudden change in maximum absorption wavelength and striking color change, as shown in FIG. 7; solvent: acetonitrile/water, in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c); concentration: BNGT 10 μM; pH: 1.9, 3.1, 4.0, 5.0, 5.8, 6.0, 6.3, 6.6, 6.8, 7.0, 8.0, 9.0, 9.8, 11.2, 12.0; the absorbance at 527 nm, 535 nm and 537 nm increased significantly. Therefore, in the three solvents (acetonitrile/water in a volume ratio of 1/99, 1/1 and 8/2), BNGT could be used as a pH colorimetric switch by means of three ways (a maximum absorption wavelength, absorbance and color).

Example 10: Speed of Response of BNGT to pH

To investigate the speed of response of BNGT to pH, adding 1 M NaOH aqueous solution to an acetonitrile/water (in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c)) solution of BNGT at pH 5.8 to adjust the pH to 6.0; measuring the UV-Vis absorption spectrum of the solution before and after the adjustment, and plotting the maximum absorption wavelength and color over time, with the results as shown in FIG. 8; solvent: acetonitrile/water, in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c); concentration: BNGT 10 μM. As can be seen from FIG. 8, when the pH changed from 5.8 to 6.0, the maximum absorption wavelengths of the three BNGT solutions quickly changed from 432 nm, 420 nm and 422 nm to 527 nm, 535 nm and 537 nm, respectively, and the color immediately changed from colorless to red.

The absorbance was plotted against time and the results were shown in FIG. 9; solvent: acetonitrile/water, in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c); concentration: BNGT 10 μM; absorption wavelength: 527 nm, 535 nm and 537 nm. As can be seen from FIG. 9, after the addition of the NaOH aqueous solution to the acetonitrile/water (in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c)) solution of BNGT, the absorbance at 527 nm, 535 nm and 537 nm reached the maximum in about 2 min and remained basically stable for the next 30 min.

Therefore, in the three solvents (acetonitrile/water in a volume ratio of 1/99, 1/1 and 8/2), BNGT could rapidly respond to pH as a pH colorimetric switch by means of three ways (a maximum absorption wavelength, absorbance and color).

Example: 11: Effect of Coexisting Ions on BNGT as a pH Colorimetric Switch

In order to understand the interference of common metal ions on BNGT as a pH colorimetric switch, Fe²⁺, Fe³⁺, Cu²⁺, K⁺, Na+, Mg²⁺, Ag⁺, Zn²⁺, Cr³⁺, Cd²⁺, Co⁺, Ni²⁺, Mn²⁺, Pb²⁺, Hg²⁺ and Ca²⁺ were added to the acetonitrile/water (in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c)) solution, and the UV-Vis absorption spectra of the solution before and after the addition of these metal ions were obtained.

First, the effect of coexisting metal ions on the maximum absorption wavelength and color of the solution was examined, with the results as shown in FIG. 10; solvent: acetonitrile/water, in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c); concentration: BNGT 10 μM, metal ions 100 μM; 1: none, 2: Ca²⁺, 3: Mg²⁺, 4: Ag⁺, 5: Pb²⁺, 6: Cu²⁺, 7: Mn²⁺, 8: Co²⁺, 9: Cd²⁺, 10: Ni²⁺, 11: K⁺, 12: Nat, 13: Fe³⁺, 14: Zn²⁺, 15: Cr³⁺, 16: Hg²⁺, 17: Fe²⁺. As can be seen from FIG. 10, the maximum absorption wavelength and color of the solutions at pH 5.8 and pH 6.0 before and after the addition of metal ions were almost unchanged. Therefore, the response of BNGT to pH in terms of the maximum absorption wavelength and color was hardly affected by the aforementioned metal ions.

Second, the effect of coexisting metal ions on the absorbance of the solution at 527 nm, 535 nm and 537 nm was investigated, with the results as shown in FIG. 11; solvent: acetonitrile/water, in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c); concentration: BNGT 10 μM, metal ions 100 μM; 1: none, 2: Ca²⁺, 3: Mg²⁺, 4: Ag⁺, 5: Pb²⁺, 6: Cu²⁺, 7: Mn²⁺, 8: Co²⁺, 9: Cd²⁺, 10: Ni²⁺, 11: K⁺, 12: Na⁺, 13: Fe³⁺, 14: Zn²⁺, 15: Cr³⁺, 16: Hg²⁺, 17: Fe²⁺; absorption wavelength: 527 nm, 535 nm and 537 nm. It can be seen from FIG. 11 that the absorbance of the solutions at pH 5.8 and pH 6.0 did not change much at 527 nm, 535 nm and 537 nm before and after the addition of the metal ions. Therefore, the aforementioned metal ions had little effect on the response of BNGT to pH in terms of enhanced absorbance.

Therefore, in the three solvents (acetonitrile/water in a volume ratio of 1/99, 1/1 and 8/2), BNGT had good anti-interference as a pH colorimetric switch by means of three ways (a maximum absorption wavelength, absorbance and color).

Example: 12: Reversibility of BNGT as a pH Colorimetric Switch

1 M HCl and 1 M NaOH were used to make the pH value of the acetonitrile/water (in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c)) solution of BNGT alternately change between 5.8 and 6.0, so as to determine the UV-Vis absorption spectrum of the solution.

First, the reversibility of response of the maximum absorption wavelength and color of the solution to pH was investigated, with the results as shown in FIG. 12; solvent: acetonitrile/water, in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c); concentration: BNGT 10 μM. As can be seen from FIG. 12, when the pH value was 5.8, the system was colorless and the absorption wavelength was small; when the pH value was 6.0, the system was red and the absorption wavelength was large. Therefore, among the three solvents, BNGT had good reversibility of response to pH in terms of the maximum absorption wavelength and color.

Second, the reversibility of response of the absorbance of BNGT to pH at 527 nm, 535 nm and 537 nm was investigated, with the results as shown in FIG. 13; solvent: acetonitrile/water, in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c); concentration: BNGT 10 μM; the maximum absorption wavelengths corresponding to the absorbance of the three solutions were 527 nm, 535 nm and 537 nm, respectively. It can be seen from the figure that the pH value alternated between 5.8 and 6.0, and the absorbance of the acetonitrile/water (in a volume ratio of 1/99 (a), 1/1 (b) and 8/2 (c)) solution of BNGT also changed circularly from small to large at 527 nm, 535 nm and 537 nm, respectively. It can be seen that the absorbance of BNGT at 527 nm, 535 nm and 537 nm also had very good reversibility of response to pH.

Therefore, in the three solvents (acetonitrile/water in a volume ratio of 1/99, 1/1 and 8/2), BNGT had good reversibility as a pH colorimetric switch by means of three ways (a maximum absorption wavelength, absorbance and color). The present invention designs and synthesizes a novel 1,8-naphthalimide derivative BNGT, which is relatively easy to prepare, can be used as a sensitive, responsive, and reversible three-way pH colorimetric switch, and can be especially applied to almost-all-water systems. 

1. A preparation method for a 1,8-naphthalimide derivative, comprising the following steps: (1) preparing an intermediate A using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials; (2) preparing an intermediate B using the intermediate A and hydrazine hydrate as raw materials; (3) preparing an intermediate C using the intermediate B and glyoxal as raw materials; and (4) preparing the 1,8-naphthalimide derivative using the intermediate C and trihydroxymethyl aminomethane as raw materials.
 2. A preparation method for a Cu²⁺ fluorescent probe system, comprising the following steps: (1) preparing an intermediate A using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials; (2) preparing an intermediate B using the intermediate A and hydrazine hydrate as raw materials; (3) preparing an intermediate C using the intermediate B and glyoxal as raw materials; (4) preparing the 1,8-naphthalimide derivative using the intermediate C and trihydroxymethyl aminomethane as raw materials; and (5) adding the 1,8-naphthalimide derivative to a solvent to prepare the Cu²⁺ fluorescent probe system, the solvent being an organic solvent and/or water.
 3. A method for detecting the content of Cu²⁺ in the system, comprising the following steps: (1) preparing an intermediate A using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials; (2) preparing an intermediate B using the intermediate A and hydrazine hydrate as raw materials; (3) preparing an intermediate C using the intermediate B and glyoxal as raw materials; (4) preparing the 1,8-naphthalimide derivative using the intermediate C and trihydroxymethyl aminomethane as raw materials; and (5) adding the 1,8-naphthalimide derivative solution to the system, measuring fluorescence intensity, and then determining the content of Cu²⁺ in the system according to a curve of relationship between the fluorescence intensity and the concentration of Cu²⁺ in the system.
 4. The method according to claim 1, characterized in that: in step (1), the molar ratio of 4-bromo-1,8-naphthalic anhydride to n-butylamine is 1:1.3, and the intermediate A is prepared using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials in the presence of the organic solvent and under the protection of nitrogen; in step (2), the molar ratio of the intermediate A to hydrazine hydrate is 1:5.3, and the intermediate B is prepared using the intermediate A and hydrazine hydrate as raw materials in the presence of the organic solvent; in step (3), the molar ratio of the intermediate B to glyoxal is 1:(13.3 to 15.5), and the intermediate C is prepared using the intermediate B and glyoxal as raw materials in the presence of the organic solvent; in step (4), the molar ratio of the intermediate C to trihydroxymethyl aminomethane is 1:(1 to 1.6), and the 1,8-naphthalimide derivative is prepared using the intermediate C and trihydroxymethyl aminomethane as raw materials in the presence of the organic solvent; the reaction temperature for preparing the 1,8-naphthalimide derivative is 25° C. to 80° C., and the reaction time is 6 h to 24 h.
 5. The method according to claim 2, characterized in that: in step (5), the organic solvent is acetonitrile; when the solvent is an organic solvent and water, the volume ratio of the organic solvent to water is less than or equal to 1/99; and the final concentration of 1,8-naphthalimide derivative is 10 μM.
 6. The method according to claim 1, characterized in that: the 1,8-naphthalimide derivative has the following chemical structural formula:


7. The method according to claim 6 further comprising: preparing a Cu²⁺ fluorescent probe, a pH colorimetric switch, pH colorimetric switch materials, a Cu²⁺ fluorescent probe system, or a pH colorimetric switch system, wherein the Cu²⁺ fluorescent probe, the pH colorimetric switch, the pH colorimetric switch materials, the Cu²⁺ fluorescent probe system, and the pH colorimetric switch system include the 1,8-naphthalimide derivative.
 8. The method according to claim 7, characterized in that: the application environment of the Cu²⁺ fluorescent probe, the pH colorimetric switch, the pH colorimetric switch materials, the Cu²⁺ fluorescent probe system, and the pH colorimetric switch system is an organic solvent and/or water environment; in the application, a final concentration of the 1,8-naphthalimide derivative is 10 μM.
 9. A method for pH colorimetry of a solution to be tested, comprising the following steps: adding a 1,8-naphthalimide solution to the solution to be tested to obtain a mixed system, then testing an ultraviolet-visible absorption spectrum of the mixed system, and completing the pH colorimetry of the solution to be tested according to color of the mixed system, ultraviolet-visible absorption wavelength, and absorbance, wherein the 1,8-naphthalimide solution includes the 1,8-naphthalimide derivative according to claim
 6. 10. The method according to claim 9, characterized in that: the concentration of the 1,8-naphthalimide derivative in the mixed system is 10 μM; when the mixed system contains an organic solvent and water, the volume ratio of the organic solvent to water is less than
 4. 11. The method according to claim 2, characterized in that: in step (1), the molar ratio of 4-bromo-1,8-naphthalic anhydride to n-butylamine is 1:1.3, and the intermediate A is prepared using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials in the presence of the organic solvent and under the protection of nitrogen; in step (2), the molar ratio of the intermediate A to hydrazine hydrate is 1:5.3, and the intermediate B is prepared using the intermediate A and hydrazine hydrate as raw materials in the presence of the organic solvent; in step (3), the molar ratio of the intermediate B to glyoxal is 1:(13.3 to 15.5), and the intermediate C is prepared using the intermediate B and glyoxal as raw materials in the presence of the organic solvent; in step (4), the molar ratio of the intermediate C to trihydroxymethyl aminomethane is 1:(1 to 1.6), and the 1,8-naphthalimide derivative is prepared using the intermediate C and trihydroxymethyl aminomethane as raw materials in the presence of the organic solvent; the reaction temperature for preparing the 1,8-naphthalimide derivative is 25° C. to 80° C., and the reaction time is 6 h to 24 h.
 12. The method according to claim 3, characterized in that: in step (1), the molar ratio of 4-bromo-1,8-naphthalic anhydride to n-butylamine is 1:1.3, and the intermediate A is prepared using 4-bromo-1,8-naphthalic anhydride and n-butylamine as raw materials in the presence of the organic solvent and under the protection of nitrogen; in step (2), the molar ratio of the intermediate A to hydrazine hydrate is 1:5.3, and the intermediate B is prepared using the intermediate A and hydrazine hydrate as raw materials in the presence of the organic solvent; in step (3), the molar ratio of the intermediate B to glyoxal is 1:(13.3 to 15.5), and the intermediate C is prepared using the intermediate B and glyoxal as raw materials in the presence of the organic solvent; in step (4), the molar ratio of the intermediate C to trihydroxymethyl aminomethane is 1:(1 to 1.6), and the 1,8-naphthalimide derivative is prepared using the intermediate C and trihydroxymethyl aminomethane as raw materials in the presence of the organic solvent; the reaction temperature for preparing the 1,8-naphthalimide derivative is 25° C. to 80° C., and the reaction time is 6 h to 24 h. 